Grass length and grazing muzzles: Why horses get hacked off

A grazing muzzle can reducea horse's feed intake by up to 80%.
Medium and long swards of grass proved more difficult for ponies wearing grazing muzzles, a recent study found. © Spillers

Research into the use of grazing muzzles to help with equine weight management has revealed that longer grass can be more difficult to graze, causing frustration-related behaviour in some horses and ponies.

Grazing muzzles have been shown to reduce the pasture intake of ponies by about 80% by significantly reducing bite size and intake. Ponies fitted with grazing muzzles may spend more time engaging in foraging and eating than their non-muzzled counterparts, yet the majority either lose weight or retain their body condition. This in turn helps reduce susceptibility to obesity and related disorders, such as insulin dysregulation and laminitis.

A horse at pasture wearing a grazing muzzle.
A horse at pasture wearing a grazing muzzle.

The new research using four mature ponies was conducted by the Waltham Equine Studies Group in collaboration with Dr Annette Longland of Equine and Livestock Nutrition Services (ELNS) in Wales. Their dry matter (DM) and water-soluble carbohydrate (WSC) intakes were measured in spring, summer, and autumn pastures on four, three-hour occasions per pony per season when fitted with or without a grazing muzzle. In addition ponies, with and without muzzles, were allowed to take 10 bites of swards maintained at different heights.

When wearing grazing muzzles pasture intake was reduced by 77% during spring and summer and by 83% during the autumn. Without muzzles the ponies generally reduced the sward length by half with the first bite but when muzzled the reduction was variable and the ponies appeared to experience greater difficulty in accessing the longer versus the shorter swards.

The short (less than 10cm), upright, grass appeared to be the easiest to eat, as leaf blades and stems protruded through the holes in the muzzle. The medium and long swards proved more difficult. They bent under the pressure of the muzzle and became flattened, causing the ponies to adopt various strategies to get to the grass. In some cases they pawed the ground to unearth the sward and access it through the muzzle. Alternatively they rammed the solid base of the muzzle hard onto the grass, causing it to buckle and make some blades or stems accessible. These were then yanked vigorously often causing the entire plant to be uprooted and eaten.

Water soluble carbohydrate levels in the sward were similar across the seasons although they were slightly higher in autumn. However, once muzzled the ponies’ intake of WSC wasn’t significantly different across the seasons; strengthening the evidence that the use of grazing muzzles is effective.

Equine nutritionist Clare Barfoot, the research and development manager at feed manufacturer Spillers, said: “While the frustration displayed when the muzzled ponies were on longer grass swards indicates that care should be taken to provide an accessible grass length, grazing muzzles remain an effective weight management tool. They allow turnout over large areas, increasing exercise and allow slow “trickle” feeding, to control weight gain and reduce the risk of obesity-related disorders, without significantly compromising the natural behaviour and wellbeing.”

Grazing muzzles must be used with care, should be properly fitted and horses and ponies should be adapted gradually to wearing them. Group and individual behaviour should be monitored closely to observe any potential concerns caused by changes to the herd dynamics. Muzzled horses and ponies should be confident in drinking and eating through their muzzles before turning them out for prolonged periods, and the devices should not be used for more than 10 hours per day. Total exclusion muzzles are not advised. Regular weight monitoring is recommended as some individuals can still gain weight when muzzled.

Effects of Grazing Muzzles on Intakes of Dry Matter and Water-Soluble Carbohydrates by Ponies Grazing Spring, Summer, and Autumn Swards, as well as Autumn Swards of Different Heights; Journal of Equine Veterinary Science 40 26-33

Medium and long swards of grass proved more difficult for ponies wearing grazing muzzles, a recent study found.
A grazing muzzle can reduce a horse’s feed intake by up to 80%. © Spillers

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